I bought my bag over a year ago and it is still as flat as a piece of wood, like it had been sitting around, empty, with a bunch of other stuff on top of it for years and years. I tried stuffing rags and holey socks that I was going to throw away in it for long periods of time, but once I take the stuff out, it goes back to being flat again. I can't wash this bag, because it has Deborah Nadoolman's autograph on the inside flap, so is there a way to expand the bag so that it doesn't deflate like a baloon whenever I take whatever it is I have in there out of it?
If not dipping, try misting it with a flower sprayer (only with water so that your bag doesn't grow ) and stuff it to keep the shape while drying. You don't need much water and will it will not ruin the autograph.